The present invention relates to a method and apparatus for separating isotopes by means of a laser.
Certain isotopes, for example those of uranium, which are distinguished from each other merely by their atomic weight, are not at all or hard to separate by known chemical or physical methods or means. Thus, it has been suggested in "Laser Focus", July 1975, page 12 to irradiate atomic uranium vapor by means of a dye laser tuned to the absorption band of a uranium isotope and to simultaneously irradiate the atomic uranium vapor by means of an ultra-violet light source, whereby a selective ionization of the absorbing isotope is accomplished so that the ionized isotope may be collected by means of a negatively charged collector. A drawback of this known method is the very small density of the uranium vapor that may be achieved, because such low density calls for a large plant volume. Another disadvantage is seen in the difficult and expensive handling of the uranium vapor, because the latter is very corrosive, especially since it must be produced at temperatures exceeding 2,000.degree. K. Another drawback of the prior art method is seen in that the radiation of the tuned laser light must take place in the visible wave length range. This is considered to be a disadvantage because lasers presently available for operation in this wave length range have a low degree of efficiency. Besides, two light sources are required for this type of prior art operation. A further separation method has been described in "Laser Focus", July 1975, page 48. In this method a high power laser is used to irradiate the molecules which contain the isotopes to be separated in the vapor phase. The wave length of the high power laser is tuned to one absorption line of the type of molecule which contains a specific isotope. It is an advantage of this prior art method that it is easy to handle the molecule vapors, whereby the pressures are within respectively about the one Torr range. Further, is possible to use IR-lasers, which operate with a high degree of efficiency. However, the just described prior art method is suitable only for separating relatively light isotopes, such as sulphur and boron. This method is not suitable for heavy isotopes, such as uranium, because the isotope shift of the spectral lines of molecules containing heavy isotopes such as UF.sub.6, is small. Another difficulty is seen in the fact that the spectra comprise a large number of spectral lines. Besides, the line width is substantial due to molecular impacts and due to a Doppler effect, whereby, for example, the spectral lines of U.sup.235 F.sub.6 and of U.sup.238 F.sub.6 molecules overlap each other. This fact prevents a selective excitation and dissociation of a particular species of molecules. In addition, the absorption of UF.sub.6 in a wave length range wherein IR-high power lasers are available, is small, whereby again an efficient isotope separation is not possible. It would also be a disadvantage to lower the temperature for the purpose of reducing the width of the spectral lines for the purpose of increasing the spectral selectivity, because lowering the temperature entails a substantial reduction in the vapor pressure. As a result, the molecular density is also lowered, whereby the absorption coefficient also becomes lower. Besides, lowering the temperature would require again unefficiently large plant volumes.